UTRAN (UMTS Terrestrial Radio Access Network) is a collective term which includes the Radio Network Controller (RNC), the 3G base stations (Nodes-B) and the air interface to the User Equipment (UE). Generally speaking, the base stations and the controller together define a radio access network (RAN); in particular, for networks which support the UMTS standard, the UTRAN is referred to the access network. Node-B handles radio channels, including the multiplexing/demultiplexing of user voice and data information. RNC is responsible for controlling and managing the multiple base stations (Nodes-B) including the utilization of radio network services. In practice, one RNC is capable of controlling a number (more than one) of 3G base stations. For clarity, hereafter, only one Node-B is mentioned.
More particularly, Node-B and RNC are communicated within the UTRAN through determined interfaces.
There are four interfaces connecting the UTRAN internally or externally to other functional entities: Iu, Uu, Iub and Iur. In particular, Iub is an internal interface which constitutes a logical connection between the Node-B and RNC. Physically Iub can be carried over one or more transport paths which connect a pair Node-B-RNC. Transport paths refer here to connections established at network and data link layers (OSI layers 2 and 3). Iub implementations are currently based on either Internet Protocol (IP) technologies or the Asynchronous Transfer Mode (ATM) in combination with the ATM Adaptation Layer Type 2 (AAL2). There are different possibilities for the physical layer, for example: one or several ATM STM-1 (OC-3) links or one STM-4 (OC-12) link, optical fibre, copper line, microwave radio links implementing T1/E1, Ethernet physical layer, Digital Subscriber Loop (DSL) physical layer, etc. Hence, current the transport networks in UTRAN provides multiple Iub paths connecting the RNC with the Node-B, for example, E1 connection plus connection by ADSL are typically used for allocation of data traffic, while voice can be assigned to another (ATM or IP) transport path.
These radio access network scenarios make difficult the traffic management for the RNC and the Node B as they have to choose the best path to transmit the traffic.
Call admission control checks whether there are resources available for the call (with voice or data content) in the radio access network. These resources are not only radio resources but also transport (usually wired) connections between the base station (Node-B) and the base station radio controller (RNC), i.e., Iub resources.
To date, the choice of the path for call admission has always followed a static strategy, which means traffic allocation to a predetermined path independently of the current traffic load in said path. Every kind of traffic, from circuit service (CS) calls, packet service (PS) R99, or HSPA calls, is always carried over the same transport path (the one previously. By doing so, it can happen that a specific type of traffic (for example, voice calls or other delay sensitive real time traffic) is locked into the assigned path which is congested, whilst there are other unassigned available paths that have free capacity.
In order to improve the Iub resource allocation in current 3G access networks a new mechanism which allows optimised selection of transport path is needed and presented as follows.